We report the results of psychophysical experiments with the so-called
barber pole stimulus providing new insights on the neuronal processes
underlying the analysis of moving features such as terminators or
line-endings. In experiment 1, we show that the perceived direction of a
barber pole stimulus, induced by line-ending motion, is highly dependent
on the spatial frequency and contrast of the grating stimulus: perceived
direction is shifted away from the barber pole illusion at high spatial
frequency in a contrast dependent way, suggesting that line-ends are not
processed at high spatial scales. In subsequent experiments, we use a
contrast adaptation paradigm and a masking paradigm in an attempt to
assess the spatial structure and location of the receptive fields that
process line-endings. We show that the adapting stimulus that weakens most
the barber pole illusion is localized within the barber pole stimulus and
not at line-endings' locations. Current models of line-endings'
motion processing are discussed in the light of these psychophysical
results.